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| Titel |
Radiative forcing of Mediterranean atmospheric aerosols derived from ground-based and satellite observations: dependence on the aerosol type and single scattering albedo |
| VerfasserIn |
Claudia Di Biagio, Alcide di Sarra, Daniela Meloni, Francesco Monteleone, Salvatore Piacentino, Damiano Sferlazzo |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036587
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| Zusammenfassung |
| The Mediterranean region is characterized by a high variability in aerosol origin,
composition, optical properties, and radiative effects. Ground-based measurements of aerosol
optical properties and surface shortwave irradiance carried out at the island of Lampedusa
(35.5Ë N, 12.6Ë E, central Mediterranean) during 2004-2007 are combined with co-located
simultaneous observations of the outgoing shortwave flux at the top of atmosphere (TOA)
derived from Clouds and the Earth’s Radiant Energy System (CERES) to derive estimates of
the aerosol radiative forcing (RF).
The shortwave aerosol RF efficiency, i.e. the forcing produced by aerosols with unit
optical depth at 500 nm, Ï, at the surface (FES), at TOA (FETOA), and in the atmosphere
(FEATM) are derived by applying the direct method, i.e., by calculating the slope of the
linear regression between the net flux and Ï over the available large dataset from
Lampedusa.
Three different particle classes are discriminated on the basis of their optical properties:
desert dust (DD), urban/industrial-biomass burning aerosols (UI-BB), and mixed aerosols
(MA). The average value of Ï is 0.31 for DD, 0.21 for UI-BB, and 0.14 for MA.
The single scattering albedo, Ï at 415.6 and 868.7 nm is estimated by combining
measurements of radiation fluxes and radiative transfer calculations. Average values of Ï
at 415.6/868.7 nm are 0.76/0.89 for DD, 0.91/0.81 for UI-BB, and 0.80/0.82 for
MA.
The daily mean aerosol forcing efficiency (FEd) at the equinox at the
surface/TOA/atmosphere is -68.9/-45.5/+23.4 Wm-2 for DD, -59.0/-19.2/+39.8 Wm-2 for
UI-BB, and -94.9/-36.2/+58.7 Wm-2 for MA. These results indicate that the atmospheric
forcing is ~30-50% of the surface forcing for DD, ~70% for UI-BB, and ~60% for
MA.
The daily mean aerosol radiative forcing, RFd, is obtained by multiplying FEd by the
mean Ï for each aerosol class. At the equinox RFd at the surface and TOA is -21 and -14
Wm-2 for DD, -12 and -4 Wm-2 for UI-BB, and -13 and -5 Wm-2 for MA. The forcings at
TOA and at the surface are largest for DD due to the high values of both forcing efficiency
and Ï. The atmospheric RFd at the equinox is +7 Wm-2 for DD, and +8 Wm-2 for both
UI-BB and MA, suggesting that the mean atmospheric forcing is approximately independent
of the aerosol type in the Mediterranean. Estimates of the maximum atmospheric
RF are derived by multiplying the atmospheric FEd at the summer solstice by the
largest aerosol optical depth for each aerosol class. The peak atmospheric RF is +35
Wm-2 for DD, +23 Wm-2 for UI-BB, and +34 Wm-2 for MA, indicating the
largest role of desert dust and MA, and a large influence on the atmospheric radiative
budget.
Cases of MA in the solar zenith angle interval 25Ë -¤ θ -¤35Ë are grouped in three
classes of single scattering albedo (0.7-¤ Ï |
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